Meso-thienyl and furyl rotor effects in BF₂-chelated dipyrrin dyes: solution spectroscopic studies and X-ray structural packing analysis of isomer and congener effects

Molecular Design of UV–vis Absorption and Emission Properties in Organic Fluorophores: Toward Larger Bathochromic Shifts, Enhanced Molar Extinction Coefficients, and Greater Stokes Shifts

“…In 12 , the thienyl group at the 8-position is surrounded by two hydrogen atoms attached at the 1- and 7-positions. Due to the relatively modest steric hindrance effect, the dihedral angle, φ, between the thienyl substituent and the BODIPY framework is only 46°, and this substituent is allowed to rotate by 43° during the excited state geometry relaxation, resulting in a large Stokes shift of 100 nm. , In contrast, by replacing these two hydrogen atoms with two methyl groups at the 1- and 7-positions to generate 13 , the contracted space around the 8-position thienyl substituent forces it to twist in its ground state, resulting in a large φ of 90° . This substituent is kept almost completely rigid owing to its neighboring methyl groups and cannot rotate in the excited state. , Moreover, this vertical alignment essentially isolates the thienyl substitute from the π-conjugated network in the BODIPY framework.…”

“…32,76 In contrast, by replacing these two hydrogen atoms with two methyl groups at the 1-and 7-positions to generate 13, the contracted space around the 8-position thienyl substituent forces it to twist in its ground state, resulting in a large φ of 90°. 79 This substituent is kept almost completely rigid owing to its neighboring methyl groups and cannot rotate in the excited state. 32,80 Moreover, this vertical alignment essentially isolates the thienyl substitute from the π-conjugated network in the BODIPY framework.…”

Development of meso-Five-Membered Heterocycle BODIPY-Based AIE Fluorescent Probes for Dual-Organelle Viscosity Imaging

“…Currently, fluorescent probes for viscosity mainly depend on molecular rotors, containing a fluorophore and a rotation group, in which fluorescence was quenched by free rotations and could be further restored through viscosity increase or steric effects with restricted rotation. Among these probes, CC double bonds have been widely used as a rotation group to construct a molecular rotor. − , Meanwhile, boron dipyrromethenes (BODIPYs), as an excellent emerging fluorophore, could potentially serve as a good candidate for viscosity imaging, attributing to its easily modified structures, tunable spectroscopic properties, and relatively high fluorescence quantum yields. − Among the reported fluorescent probes for viscosity, except the commonly used CC − or CC , bonds as the rotation positions, some novel meso -substituted BODIPY derivatives have aroused more interest recently, such as CF 3 , , benzothiazole, CO, , and phenyl groups. − It is worth to mention that some other meso -five-membered ring-substituted BODIPYs have also been reported for their spectroscopic properties or as fluorescent sensors for oxidants and metal ions. − The abovementioned meso -substituted BODIPY-based molecules for viscosity not only displayed good responsive properties toward viscosity but potential aggregation-induced emission (AIE) has also been discovered, which might be helpful in cellular imaging to avoid aggregation-caused quenching (ACQ) and increase sensitivity. − Our group reported a meso -CF 3 BODIPY-based AIE rotor for successfully detecting mitochondrial viscosity . Recently, a meso -benzothiazole BODIPY has been investigated by us, which showed good viscosity response in lysosomes without the morpholine ring and AIE in 70% aqueous solution .…”